It is known in the art that octane values or antiknock properties of hydrocarbons can be improved by catalytic reforming process. There is a need to increase the antiknock quality of straight run and naphtha-type gasolines to obtain blending stocks for motor fuels, e.g., to blend with alkylate gasolines, and the like, to produce high octane motor fuels. Catalytic reforming is one method of increasing the octane values of these low antiknock hydrocarbons.
Usually the feedstocks to reforming are pretreated to remove catalyst poisons such as arsenic, sulfur, and nitrogen compounds, which extends considerably the life of the reforming catalysts.
Catalysts which are used in reforming can cause side-reactions, or undesired reactions when maximizing of gasoline is desired, such as hydrocracking. Higher pressure in the reformer will suppress hydrocracking, but higher pressure also suppresses dehydrogenation of the naphthenics and results in lower octane products. Currently used reforming catalysts include platinum-on-alumina, and multimetallic catalysts having platinum along with other metals such as rhenium. The prior art discloses many reforming catalysts.
Halogen, such as chloride, is desirable in the reforming operation to effect proper isomerization of low octane normal paraffins to higher octane isoparaffins. Too much chloride, however, causes too great an amount of hydrocracking which is, of course, not desired.
A number of reactions occur during reforming including dehydrogenation of naphthenics to aromatics, some of which aromatics are excellent petrochemical feed materials, with the major amount of aromatics being used as high octane gasoline components for blending into gasoline products. Other reactions occurring in reforming include cyclization of paraffinic hydrocarbons, which are then dehydrogenated to aromatics; isomerization of paraffinics; and hydrocracking which decreases the yield of gasoline and produces lighter hydrocarbons including methane, ethane, propane, butanes, and pentanes.
Hydrogen is a by-product of reforming (dehydrogenation occurs). Some hydrogen is recycled to reforming to sustain pressure and to mainly suppress coke formation (which results from hydrocracking). The net or yield hydrogen is available for use in hydrocracking, hydro-treating (hydrodesulfurization, hydrodenitrification), hydroisomerization, and to manufacture certain chemicals.
Since the halogen concentration in the reforming operation has a direct influence on the product composition, it would be desirable to have means to control the halogen content by manipulating halogen addition to the reformer responsive to the control signal. The faster the response of the control signal to a change in the halogen content is the more accurate the control can be and the more desirable the results achieved will be.